docs: def dump(self, fname):
          """
          Dump the remote datastore on a local path.
          """
          url = '%s/v1/calc/%d/datastore' % (self.server, self.calc_id)
          resp = self.sess.get(url, stream=True)
          down = 0
          with open(fname, 'wb') as f:
              logging.info('Saving %s', fname)
              for chunk in resp.iter_content(CHUNKSIZE):
                  f.write(chunk)
                  down += len(chunk)
                  println('Downloaded {:,} bytes'.format(down))
          print()